FabLab IRBID

Computer-Controlled Machining

We use in FABLAB Irbid , a ShopBot PRSalpha CNC . which have high performance, high volume, speed and reliable power for all cutting tasks.

For the group assignment we tested the Runout for the spindle and the difference between the resulting cuts when changing the feed and the speed for the same part.

Spindle Runout

Runout is a rotation inaccuracy which occurs when the tool is no longer aligned with the main axis. In drilling applications, this can result in a bore diameter that is actually larger than the drill’s nominal diameter.

To test the Runout we used a sensitive dial gauge indicator, which its accuracy measured in 0.01 mm. fixed it to the table and the tip should touch the spindle.

First we tested the runout for the spindle itself, where we selected an empty area and fixed the dial indicator tip, see the below video.

You can notice from the video that the indicator moves very small motion, to be able to analyze this motion and rad the measurement value , lets first explain the dial gauge indicator. the circular in this gauge is divided into two symitrical parts, each has segments from 0 to 40.

The 0.01 means that each small step from the 0 equals 0.01 mm, which means that the large step (10) equals 0.01*10 = 0.1 mm. So, as we saw in the video our indicator moved only one step from the starting point this means that the Runout for the spindle equals 0.01mm. which considered good for this machine.

After testing the Runout for the spindle, we tested the runout for the tool attached to the spindle, to make sure that it the tool is attached probably to the spindle (without any angles).

See video Below

When looking to the dial indicator perpendicular to its face, we can read that the measure .02mm from the first point.

Feed and Speed

The second thing we tested was the effect of the speed and feed on the result cuts in the CNC on a plywood board. To do that we drew 6 circles on V-carve, and created a separate toolpath for each of them, changing each time the value of the tools speed and feed, see below images.

And send them to the shopbot and cut them, see below results

Conclusion

From the images we can notice that for the same speed, always the circle with higher feed has a better finish, but the higher feed with the higher speed gave the most satisfying resulting.

So , as you increase the feed and the speed, you increase the quality of the resulting. Considering the material you’re using .